Our system handles this for you by treating memberships as subscriptions. If you are a current member and you are logged in, purchase of a membership is treated as a renewal and begins upon expiration of your current membership subscription. If you are not a current member your purchase is considered a new membership which begins immediately.
Therefore, if you are a current member it is imperative that you are logged in to get a renewal. Please login and visit My Account to verify that you are recognized as a member before renewing your membership.